The objective of this project is to define key parameters involved in transgenerational inheritance of alterations in the function of the mammalian immune system that occur as a result of environmental exposure. The immune system is fundamentally important to public and individual health, and even slight modifications in its function can have a profoundly negative impact on health and disease. For instance, influenza virus infections pose significant global health threats, infecting over 1 billion people annually. Evidence points to prenatal and early life exposure to pollutants as overlooked contributors to poorer clinical outcomes following influenza and other respiratory infections. One family of environmental agents for which there is evidence that developmental exposure affects the function of the immune system in humans and animal models is aryl hydrocarbon receptor (AhR) ligands. For instance, early life exposure to the prototype AhR ligand, 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) profoundly disrupts the response of specific lymphocyte subsets to infection in the F1 generation, and exciting pilot data reveal that lymphocyte function is affected in F2 offspring. Other preliminary data support the idea that these changes are due, at least in part, to alterations in DNA methylation. Moreover, TCDD causes transgenerational (F3) effects and altered DNA methylation in other organ systems. Using contemporary, sensitive assays that directly relate to disease outcome, we will further characterize an integrated set of disease-specific T cell responses in the F3 generation, and directly compare these changes to the modified anti-viral immune response observed in F2 and F1 offspring. This comprehensive analysis will include defining the dose-dependent nature of transgenerational effects on T cell functions, and establishing the ligand-specific nature of immune function changes across generations. We will also define the developmental window of susceptibility, basis of sex differences, and role of parental origin in transgenerational inheritance of altered immunity to viral infection. Moreover, we will investigate the mechanism by which AhR ligand exposure transmits aberrant immune function from one generation to the next. We will identify genes and gene networks that are altered in a transgenerational manner using genetic, pathway-specific and genome-wide approaches, and link these changes to alterations in DNA methylation and other epigenetic regulatory mechanisms. The new scientific information generated will have a tremendous impact on public health. Few studies of transgenerational inheritance of the effects of environmental exposures have considered the immune system, or directly evaluated the potential consequences to a disease that affects at least 1 in 7 people each year. Given that TCDD and other AhR ligands cause developmental and transgenerational effects in other tissues, findings from our studies will have a broad impact on efforts to better predict the potential for AhR and its myriad ligands to impinge on many facets of human development and health.